💡 let a colordepth "16" event switch a live term to 16 colors #153

Is your feature request related to a problem?

on #148, a colordepth capability event only folds into trueColor (color-encoding-spec §6.1: "no other fold changes the tier"). so colordepth: "256" works at runtime, but colordepth: "16" just turns truecolor off and leaves colors alone, and the term keeps emitting 256-color SGR. the only way to get real 16-color output is to create a new term

repro (pinned to #148's preview build): https://stackblitz.com/edit/stackblitz-starters-9nffjdmq?file=index.js

it renders red text, then folds colordepth events into the same term:

• start (truecolor): 38;2;255;0;0
• after colordepth: "256": 38;5;1
• after colordepth: "16": 38;5;1, still 256
• a new term created with colors: 16: 31

Describe the solution you'd like

let colordepth: "16" fold into colors too, so the event value is the tier you get. it's still capability evidence going through update(), so it fits TINV-3 without adding a separate color mode option

Describe alternatives you've considered

rebuilding the term on a tier change, which is what my command palette demo does. it works, but the caller has to carry the theme, sync-output and pointer-shape state over by hand and restore the pointer shape first. i got that wrong the first time and pointer shapes stopped working after any tier switch, so it's easy to trip on

Additional context

related to #60 and #148. the compositing demo on feat/compositing-core has the same issue: its 3 key folds colordepth: "16", and after pressing it the demo only emits 256-color SGR (no 16-color codes)

AI assistance disclosure

• This feature request was drafted with the assistance of an AI tool.